Maybe a little stiff but not imo toooooooo stiff. I shoot a widow psaII 53# at 29" i shoot for hunting easton FMJ 340 spine cut to 30" with 75 grain brass insert and 125 grain silver flames, 200 grains total up front, They bareshaft perfect and broadheads group right on with the fieldpoints.
for competition I use woods cut to 29.5 inches 75-80 spine with 165 grains up front (125 grain point and 40 grain top hat adapter)
They fly like darts and bareshaft perfect too, In fact I just won the Norwegian field archery champs (FITA) trad class so I know they work
Widows like stiff arrows
There are alot of variables to think of, everyone shoots a little differently so spine can be up to a point a personal thing too.
Now you say that you have banana fletching on the arrows, but is there enough helical,or even any at all? I have seen finished arrows sold in shops wit no helical at all, no problem for field points, but BHs need helical...
In your quest to find the problem adjust only one thing at a time.
Much can be done by adjusting the brace height, I find my widow like a brace height of between 8 3/4 " and 8 7/8 " any less than this will result in bad groups, especially with BHs
If the arrows were too stiff, in my experience they would have a tendancy to hit left with broadheads..
Good luck in finding the solution..
regards, Nathan